Generally, a variety of methods are known as noise countermeasures. For example, a remote monitoring apparatus is disclosed, which is provided with various sensors inside a control panel and determines, based on data acquired from these sensors, whether an environment inside the control panel is abnormal or not (see PTL 1).
A data collection system is also disclosed, which measures data of physical quantities such as a voltage or current of an electronic apparatus using a plurality of detectors set up in places away from each other, transmits the data to a data collection apparatus through a wireless system, and can collect measured data of the respective detectors at an identical time with an accuracy of 10 nanoseconds or less (see PTL 2).
On the other hand, when an electric wire such as a signal line or DC power line is laid, a noise source such as a relay may be connected to the electric wire. Alternatively, an electric wire including a noise source may be laid in the vicinity of another electric wire and noise may be superimposed on the nearby electric wire by induction. However, there are also electric wires which are laid without a possibility of noise being applied or noise being superimposed by induction. In that case, noise may cause misoperation or the like in an apparatus using the electric wire.
Examples of noise countermeasures include prevention of transmission or induction of noise, increase of noise resistance in apparatuses and measures against noise sources.
Prevention of transmission or induction of noise is often adopted as noise countermeasures, but this involves the following problems. Noise is transmitted in three ways: induction, transmission and electromagnetic wave. Therefore, influences of noise may appear in different places even when certain countermeasures are adopted. Taking full countermeasures requires operation including experience and knowledge, and so a plurality of action plans are executed on a cut-and-try basis, and it takes time until it becomes possible to confirm the results.
For example, a method of shielding an electric wire and leading noise to ground is available as a noise countermeasure. With this method, however, a ground may become a transmission medium of noise from other noise sources or the ground may not have an impedance characteristic low enough to allow a sufficient high frequency current to flow, failing to serve as a noise countermeasure.
On the other hand, increasing the noise resistance of the apparatus requires a cost increase on the apparatus side as a noise countermeasure, and it is often the case that this measure cannot be adopted.
Thus, one of fundamental noise countermeasures is a countermeasure taken on noise source side. Examples of the countermeasures on the noise source side include removal of the noise source and prevention of noise output from the noise source. However, it may be impossible to remove the noise source. For example, the noise source is attributable to a natural phenomenon such as lightning or a breaker or the like to protect devices.
However, in order to take countermeasures on the noise source side, the position of the noise source needs to be identified. A distance over which a noise-carrying electric wire is laid may be as far as several hundreds of meters. Furthermore, the location where an electric wire is laid is often a place where many other electric wires exist such as under a floor or a switchboard. Therefore, identifying the position of the noise source is not easy work.